1. Field of the Invention
The present invention relates to a storage apparatus such as a magnetic disk apparatus, control method, and storage control circuit which subject a head to seek control to a target track of a storage medium and positions it thereon and, particularly, relates to the storage apparatus, control method, and control device which perform seek control while compensating for rotation disturbance vibrations applied to the apparatus.
2. Description of the Related Arts
Conventionally, in a magnetic disk apparatus, when a read command or a write command is received from a host, seek control in which a head is positioned from a current track position to a target track of a magnetic disk specified by the command is performed by driving a rotary actuator by a voice coil motor. The seek control can be divided into coarse control (rough control) and fine control (precise control). In the coarse control, a target velocity pattern which increases the velocity, keeps a constant velocity, and reduces the velocity according to the number of remaining tracks from the current track to the target track is generated, and velocity control is performed so that the head moving velocity follows the target velocities; and, at the point when it is in the vicinity of the target track, it is switched to the fine control. More specifically, when the number of remaining tracks reaches a predetermined value during the velocity control following the target velocities, it is switched to the fine control if the condition that the head position is within the range of fine switch slice with respect to the target track is satisfied. At this point, if the head is out of the predetermined range of fine switch slicing set for the target track, a seek error (hereinafter, referred to as a “coarse seek error”) is determined, the head is returned to a starting track, and seek retry in which seek control is performed again is performed. The fine control is stabilization control (settling control) for making a transition to following control by leading the head position signal demodulated from servo information of the magnetic disk to a target track center. Regarding the fine control, predetermined settling time and fine completion slices are set, seek completion is determined and transition to following control is made if the head position is within the range of the fine completion slices when settling time is elapsed, and an on-track flag is set so that a read operation or a write operation based on the command can be executed. If the head position is out of the range of the fine completion slices when the settling time is elapsed, it is considered to be a seek error (hereinafter, referred to as a “fine seek error”) due to time out of the settling time, the head is returned to the starting track, and a seek retry in which seek control is performed again is performed as well as the case of the coarse seek error in the coarse control. However, in the usage environment of a magnetic disk apparatus, it is housed in a rack of, for example, a server or a storage system; therefore, it is affected by the vibrations of a fan or another magnetic disk apparatus. These vibrations physically vibrate the rotary actuator, and the vibrations appear as disturbance in the head position signal. The vibrations applied to the magnetic disk apparatus include translation vibrations and distortion vibrations. The translation vibrations are the vibrations that move the entire apparatus in one direction and do not affect head positioning since the rotary actuator is also integrally vibrated. On the other hand, the distortion vibrations are the vibrations that move the entire apparatus in a rotating direction about a certain position, are the vibrations that move the rotary actuator, which is rotatably supported by a pivot shaft, in the rotating direction, and serve as disturbance that causes a head positioning error; and these are referred to as rotation disturbance vibrations. In order to eliminate deterioration of the positioning accuracy due to such rotation disturbance vibrations, in a conventional magnetic disk apparatus, an acceleration velocity sensor that detects disturbance vibrations is provided, and feed forward control of canceling them out by adding a servo compensation signal proportional to the output of the acceleration velocity sensor to a seek control servo system is performed, thereby reducing the head positioning error caused due to foreign vibrations even when unexpected rotation disturbance vibrations are applied from outside (JP63-213176). Such disturbance vibrations are also applied to the seek control, in which the head is moved and positioned to a target track, as disturbance and deteriorate the positioning accuracy of the seek control. Therefore, the servo compensation signal detected by the acceleration velocity sensor is added also to a seek control system so as to cancel out the disturbance vibrations, thereby reducing the positioning error of the seek control.
However, in the conventional rotation disturbance compensation control using the acceleration velocity sensor, the signals output from the acceleration velocity sensor contain noise components due to factors other than rotation disturbance vibrations in some cases, and there is a problem that the positioning accuracy of the seek control is deteriorated due to the influence of the noise components contained in the compensation signal of the rotation disturbance vibrations added to the seek control system. More specifically, the acceleration velocity sensor used in the rotation disturbance compensation control is expected to detect rotation disturbance vibrations in the disk surface (X-Y plane) of the magnetic disk apparatus; however, in practice, the output of the acceleration velocity sensor contains power source ripple noise or disturbance components other than rotation disturbance vibrations due to translation vibration in the direction (Z direction) orthogonal to the disk surface, an inappropriate sensor signal is fed forward to the seek control system as a result, and the control accuracy is deteriorated, which is a problem. Moreover, there is also a problem that, even in a normal case in which disturbance vibrations or noise are not applied to the acceleration velocity sensor, the sensor signal contains noise components due to the influence of the S/N ratio of the acceleration velocity sensor itself, and the control accuracy is deteriorated when such sensor signal is fed forward to the seek control system.